Manufacturing and conditioning of solid solution organic pigments

ABSTRACT

Organic solid solution pigments are prepared and conditioned by treating a mixture of their components, after synthesis but perferably without or with only partial drying, in a mixture of from 0 to 30% by weight of an organic liquid having a dipole moment μ of 2.8-6.0·10 −18  .esu (2.8 to 6.0 debye units) and from 70 to 100% by weight of water in an agitated media pearl mill having a specific power density of at most 2.0 kj·s −1  per litre of grinding space. Drying the starting components is especially suitable in the case of only slightly agglomerating, easy to wet pigments of specific surface area from 1 to 25 m 2 /g. The method gives excellent results, and is flexible and also much simpler than known methods.

The invention relates to a simplified, economical and environmentallyfriendly method of preparing and conditioning solid solutions and mixedcrystals of organic polycyclic pigments, especially quinacridones anddiketopyrrolopyrroles. The coloristic properties of the solid solutionpigments obtained are significantly improved and much better than in thecase of existing simple methods, while the use of known methods that aremore complicated, more costly or problematic can advantageously beavoided.

Pigments are generally obtained from synthesis in a form that is notsuited, or is only poorly suited, to most applications. It is thereforecustomary for the crude pigments to be subjected to conditioning. In thecourse of time it has also been found that most conditioning methods arehighly specific and can be used only for individual pigment classes oreven only for individual pigments, giving rise, therefore, to virtuallycountless methods, which have been disclosed in a very large number ofpatent applications and patents.

In such methods, the same basic principles are always applied: the crudepigments are dissolved and re-precipitated from the solution, ground(where appropriate, with the aid of grinding elements), or treated withwater or solvents (where appropriate, at elevated temperature). Thesemethods are generally combined with one another and, where appropriate,supplemented by additional process measures having different purposes,for example the addition of acids, bases and/or additives, giving riseto the many known variants.

The patents and patent applications which are considered in detail inWO-02/068541 (published after the instant application's priority date)appear representative of those existing general methods, for examplethose described in EP-A-0 524 904, EP-B-0 737 723, EP-A-0 971 001,JP-A-54/130621, JP-A-58/147461, U.S. Pat. No. 2,857,400, U.S. Pat. No.3,017,414, U.S. Pat. No. 3,256,285, U.S. Pat. No. 3,615,800, U.S. Pat.No. 4,024,148, U.S. Pat. No. 4,247,696, U.S. Pat. No. 4,431,806, U.S.Pat. No. 4,734,137, U.S. Pat. No. 4,895,948, U.S. Pat. No. 4,895,949,U.S. Pat. No. 4,922,101, U.S. Pat. No. 5,264,034, U.S. Pat. No.5,318,627, U.S. Pat. No. 5,428,136, U.S. Pat. No. 5,492,563, U.S. Pat.No. 5,565,578, U.S. Pat. No. 5,614,014, U.S. Pat. No. 5,756,691, U.S.Pat. No. 6,191,263 and WO-A-99/54410.

Often, pigments are first dissolved to produce clear solutions, forexample in concentrated sulfuric acid or a highly polar solvent such asdimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone with theaddition of a small amount of a strong alkali (at most 20% water, basedon the liquid phase). The solution of colorant is then diluted withdilute acid, water or an alcohol or is added thereto, the crystallineform obtained being critically dependent upon the precise precipitationconditions. For example, diketopyrrolopyrroles, perylenes andquinacridones can be treated in that manner. The pigments may also bedissolved only in part (Ostwald ripening).

However, such recrystallisation methods promote the growth of purecrystals and/or phase changes, so that they are only exceptionallysuitable in the case of solid solutions and mixed crystals, which have afine-tuned crystal lattice easily disturbed through conditioning.

According to U.S. Pat. No. 4,094,699, organic liquids need not be usedduring wet grinding of quinacridones if a wetting agent together with astrongly alkaline aqueous solution is used. No solid solution ismentioned.

U.S. Pat. No. 3,287,147 discloses the formation of mixed crystals ofquinacridones by acid pasting the mixture of the components followed byheating a neutral aqueous slurry of the product at from 150 to 300° C.,preferably 220 to 270° C. for 12 to 36 hours in an autoclave andextraction with sulfuric acid to remove traces of iron.

U.S. Pat. No. 4,783,540 describes how, starting from a physical mixtureof two different 1,4-diketo-2,5-dihydro-pyrrolo[3,4c]pyrroles, it ispossible to obtain solid solutions by kneading, grinding,reprecipitating or contacting the mixture with polar solvents. U.S. Pat.No. 4,810,304 discloses the same methods to prepare mixeddiketopyrrolopyrrole/-quinacridone solid solutions, which are optionallyconditioned in n-butanol.

The X-ray diffraction diagrams of these solid solutions are in bothcases different from the sum of the X-ray diffraction diagrams of theindividual components. In all of the products obtainable in accordancewith the disclosed examples, however, they are also markedly differentfrom the X-ray diffraction diagrams of the pure crystalline individualcomponents. The solutions involved, therefore, are exclusivelymultiphase solid solutions, which have no definite, uniform crystallattice such as in a mixed crystal of uniform crystal lattice or asingle-phase solid solution wherein the guest entirely disappears intothe host's crystal lattice. Moreover, these products are with fewexceptions obtained in an undesirable, largely amorphous form.

Example 11 of U.S. Pat. No. 5,194,088 discloses a process for thepreparation of a solid solution of1,4-diketo-2,5-dihydro-3,6-di(4-chlorophenyl)-pyrrolo[3,4c]pyrrole and2,9-dichloroquinacridone consisting of premilling the mixture of crudepigments and then growing crystals by heating in N,N-dimethylformamide.

An analogous method is used in DE-OS 1 810 817 to produce solidsolutions of perylenes from very fine dispersions. In the examples,preliminary comminution is performed by coprecipitation or preferably bymixed synthesis.

EP-A-0 101 163 discloses a process for the preparation of finished solidsolution quinacridone pigments from crude precursors by two-stepmilling, first dry then with a basic aqueous solution comprising from 5to 25% by weight of an organic liquid. This process is very slow.

U.S. Pat. No. 5,756,746 discloses single-phase solid solutions ofdiketopyrrolopyrroles or diketopyrrolopyrroles/quinacridones, obtainedpreferably but in unsatisfactory low yields through alcalinereprecipitation or from mixtures of pigment precursors. The otherdisclosed but not exemplified methods of U.S. Pat. No. 4,783,540 andU.S. Pat. No. 4,810,304 are manifestly less satisfactory.

JP-A-2001/154387 and WO-02/04563 disclose solid solutions, respectivelymixed crystals, comprising as guests some of the instant pigments. Inboth cases, the main component (host) is a phthalocyanine, but theguests are from different pigment classes.

All these methods are, for various reasons, not entirely satisfactory;moreover, such methods can be transferred from one pigment to anotheronly with difficulty and sometimes fail entirely to form solidsolutions, as disclosed in EP-0 737 723 and WO-00/56819. In the case ofmultifunctional pigment plants, that results in high investment costs, ahigh personnel requirement, a lack of operational flexibility andextremely complex and costly quality assurance measures. The use ofstrong acids and high boiling point polar solvents in high quantities isproblematic and their disposal or recycling is costly, too.

Some of those problems can be avoided in certain cases by subjecting thedry crude pigments to salt kneading in a separate system with theaddition of a small amount of solvent. The procedure is, however, slow,noisy and very energy-consuming, and it is not applicable to all soughtsolid solutions and mixed crystals. In addition, because of the veryhigh frictional energy, it is necessary to monitor continuously thetemperature (with a great deal of cooling) and the viscosity of thepaste and, subsequently, solvent-containing brine must be disposed of inan environmentally friendly manner. In addition, further purificationsteps are necessary to achieve the low conductivity required, forexample, for electronic applications, and a preliminary amorphisation ofone component may be necessary as disclosed in WO-02/04563.

There has now been found, surprisingly, a simple combined preparationand conditioning method which can be used for a large choice of organicsolid solution pigments and which ensures a very high quality of finalproduct together with a considerable increase in productivity.

The invention accordingly relates to a method for the preparation of aconditioned organic pigment comprising at least a first componentselected from the group consisting of 4,4′-diamino-1,1′-dianthraquinonyls, diketopyrrolo[3,4-c]pyrroles, triphenedioxazines,indanthrones, perylenes, phthalocyanines and quinacridones, and a secondcomponent forming a solid solution or a mixed crystal with the firstcomponent, the molar ratio of the first component to the secondcomponent in the solid solution or mixed crystal being greater or equalto 1, wherein

-   -   (1) the first component and the second component are each        independently from the other so synthesised that they        precipitate from a liquid reaction mixture, and a pigment        suspension is formed in the liquid reaction medium;    -   (2) optionally, the concentration of pigment in one or both        pigment suspensions from step (1) is increased by removing all        or part of the liquid reaction medium;    -   (3) optionally, a washing agent is added once or more than once        and then the concentration of pigment in one or both pigment        suspensions from step (1) or (2) is increased by removing all or        part of the liquid phase;    -   (4) optionally, the pigment suspension is dried;    -   (5) the pigment suspensions from step (1), the concentrated        pigment suspensions from step (2), or the pigment suspensions        (treated with a washing agent and concentrated) from step (3),        the liquid phases of which consist substantially of water, an        organic liquid or a mixture thereof, or the dried pigments from        step (4) are each transferred into a storage vessel or both        transferred into the same storage vessel, optionally with        addition of water or an organic liquid, preferably keeping the        pigment surface substantially wetted with liquid reaction        medium, washing agent, organic liquid or water all the time;    -   (6) if the liquid phase of the pigment suspension in one or both        storage vessels does not already consist of water and optionally        an organic liquid, the amount of organic liquid being from 0 to        50% by weight, based on the total amount of organic liquid and        water, the composition of the pigment suspension is so modified        by means of the addition of water that the amount of organic        liquid is from 0 to 50% by weight, based on the total amount of        organic liquid and water; and/or optionally organic liquid is        added in such quantity that its total amount does not excede 50%        by weight, based on the total amount of organic liquid and        water;    -   (7) the pigment suspension from the storage vessel containing        the first component and if applicable the pigment suspension        from the storage vessel containing the second component are        passed a number of times through an agitated media pearl mill in        a circulating or shuttle mode of operation, the agitated media        pearl mill having a smaller chamber volume than the volume of        the pigment suspension and being operated at a specific power        density of at most 2.0 kj·s⁻¹ per litre of grinding space,        whereby in case of more than one storage vessel the flow between        the storage vessels and the pearl mill is controlled in such a        way that the contents of all storage vessels are mixed together        at any stage up to before the last pass in the pearl mill;        whereby the first component and the second component combine to        form a solid solution or a mixed crystal;    -   (8) optionally, the concentration of pigment in the pigment        suspension from the agitated media pearl mill is increased by        removing all or part of the liquid reaction medium;    -   (9) optionally, a washing agent is added once or more than once        to the pigment suspension from step (7) or (8) and then the        concentration of pigment in the pigment suspension is increased        by removing all or part of the liquid phase; and    -   (10) optionally, the pigment is isolated by removing the liquid        surrounding it.

Step (1) corresponds to pigment synthesis known per se to the personskilled in the art but stopped at the point where the reaction iscomplete. Subsequent maturation may optionally be carried out, forexample in order to increase filterability, but that should be carriedout under mild conditions so that the pigment particles do not becometoo large. Generally, the average size of non-agglomerated primaryparticles, viewed with an electron microscope, should be from 0.01 to 3μm, preferably from 0.05 to 2 μm. It is generally much preferable thatthe pigment particles are not dried; otherwise, they aggregate and thedesired result cannot be achieved or is achieved too slowly.

Although not desirable, it is nevertheless possible to use a driedpigment, or to perform step (4), in particular in the case of verycoarse pigments that have only a very slight tendency to aggregate andare easy to wet with water or a polar solvent, for example crudepigments having a specific surface area of from 1 to 25 m²/g, especiallyfrom 2 to 15 m²/g. Dried pigments preferably still comprise a residualamount of water or an organic liquid, for example from 0.1 to 20% byweight, most preferably from 1 to 10% by weight. Apart of the additionaldrying and wetting steps, however, this procedure is in all particularssimilar to that described above and the same preferences do apply.

Increasing the concentration of pigment in the pigment suspension insteps (2), (3), (8) and/or (9) can be carried out by methods known perse, for example filtration, dialysis or sedimentation with removal ofliquid from the clear phase, optionally under increased gravity. ‘Part’is to be understood as an amount of from 1 to 99% by weight, usuallyfrom 1 to about 90% by weight.

Washing agents suitable for step (3) are known to the person skilled inthe art from the relevant synthesis methods for the pigment used. Theyare, for example, water, brine, bicarbonate solution or any desiredorganic solvent, alone or in admixture or in any desired order. Thepurpose of such washing is to remove unreacted starting materials,reagents and by-products, especially acids, bases and colouredimpurities. If filtration is used in step (2), it is especiallyefficient and advantageous to rinse the wet filter cake with washingagent. It is of course also possible first to redisperse the filter cakein the washing agent and only then to filter again.

The pigment suspension can be transferred to the storage vessel bymethods known per se, which will depend on the consistency of thepigment suspension. A low-viscosity pigment suspension can, for example,be pumped, a solid press cake can be transferred by scooping or tipping,and a viscous paste by flushing with water or solvent. A particularaspect of the invention relates to transferring the pigment suspensionin the form of a press cake consisting of from 10 to 50% by weightpigment and from 50 to 90% by weight liquid, preferably from 20 to 40%by weight pigment and from 60 to 80% by weight liquid. In that case theliquid is an organic liquid, water or a mixture thereof, preferablywater.

Of course, steps (2), (3) and (4) can be performed or omitted for eachcomponent entirely independently from their realization or omission forthe other components.

Step (6) specifies suitably modifying, when necessary, the ratio ofwater to organic liquid before passage through the agitated media pearlmill. If an organic liquid is added in step (6), that is carried outpreferably before step (7) is started. It is also, however, perfectlypossible to add all or some of the organic liquid to the pigmentsuspension only after one or more passes through the agitated mediapearl mill, although the treatment time will be needlessly extended as aresult. However, the instant ratio of water to the total quantity oforganic liquid must be respected.

The treatment of the pigment suspension in the agitated media pearl millis the essential step of the invention. Surprisingly, step (7) leads toformation of solid solutions or mixed crystals in a much easier andbetter way, as compared with prior art methods. Suitably, the singlecomponents of the solid solution to be formed can be mixed at any stageof this step, for example already before or just at the beginning orafter a few passes, but a homogeneous mixture should of course beachieved no later than before the last pass, preferably before the lastthird of the total grinding time. Means of mixing are for examplestirring, pumping or pouring from one storage vessel to another ofdifferent contents, inlet from the pearl mill to a storage vessel ofdifferent contents or simultaneous inlet from storage vessels ofdifferent contents to the pearl mill in any volume ratio. However, it isalso possible first to pass the suspensions from one or more of thestorage vessels any number of times separately through the pearl millbefore mixing them. This provides an opportunity to optimize particlesize and shape of the different components before the preparation ofsolid solutions or mixed crystals is started, leading to outstanding andhighly reproducible results.

The friction should preferably not be too high; otherwise, pigmentparticles that are obtained will be too small as a result of thegrinding action. Conversely, the speed should preferably not be too low;otherwise, the dispersive force will be insufficient to separate anyagglomerations present into their primary particles. For excellentresults, it has been found that the specific power density should be atmost 2.0 kj·s⁻¹ per litre of grinding space and the peripheral speed ofthe agitator should then be from 5 to 12 m·s⁻¹, preferably from 6 to 11m·s⁻¹. Higher peripheral speeds of up to about 15 m·s⁻¹ (perhaps evenhigher in the future) are possible with some special apparatus, but onlyif achievable at a specific power density of at most 2.0 kj·s⁻¹ perlitre of grinding space.

The temperature is advantageously in the range between the freezingpoint and the boiling point of the mixture of water and organic liquid,preferably from 10 to 120° C., especially from 60 to 100° C. or alsofrom 100 to 120° C. under excess pressure. The temperature isadvantageously adjusted in the storage vessel. An especially preferredaspect of the invention, however, relates to starting step (7) at atemperature of from 10 to 50° C., preferably from 15 to 45° C., thenoptionally to rise the temperature (at once, gradually, or in steps) inthe course of grinding to a value of from 30 to 100° C., preferably from50 to 100° C. at the end of step (7). Temperature control can beachieved especially conveniently in the temperature range from 30 to100° C., because the heat of friction can be balanced, approximately, bythe heat losses. Above that range, it is necessary to carry out heating.After the solid solution or mixed crystal has been formed, it isoptionally also possible to ripen it outside the pearl mill. It is alsopossible to decrease the temperature as disclosed in WO-02/068541.

The agitated media pearl mill is a known apparatus, it merely beingadequate to use a controller so that, at full power, it does not exceedthe above-mentioned specific power density. Whilst taking thatprecaution, it is possible to use any desired apparatus, withoutrequiring any special constructional measures because the heat offriction is not very great. In other regards, the operating instructionsof the available apparatus should be consulted. As grinding elementsthere are used, for example, balls of from 0.1 to 1 mm in diameter madefrom zirconium oxide, mixed zirconium oxide, aluminium oxide, quartz ora metal such as steel, preferably mixed zirconium oxide balls having adiameter of from 0.2 to 0.3 mm.

The total treatment period in the agitated media pearl mill is usuallyfrom 10 to 600 minutes, preferably from 20 to 200 minutes (includingdwell time in the storage vessel between individual passes), a longertreatment period such as up to 10000 minutes having no significanteffect on the properties of the product. As a result, the risk ofovermilling can be excluded, with very great advantage for the meetingof specifications, especially if it is ensured that the radial speed ofthe mill is not too high; in the final phase of grinding (approximatelythe last third of the total grinding time), the radial speed should becut back to a value of at most 11 m·s⁻¹, preferably from 1 to 8 m·s⁻¹,especially from 2 to 5 m·s⁻¹.

In the case of a shuttle mode of operation, a plurality of storagevessels is used, for example from 2 to 20 storage vessels, thesuspension being passed from one storage vessel to another storagevessel via the agitated media pearl mill. The flow between the differentparts of the equipment can be kept constant, or it can changed once ormore times, manually or automatically or preferably by computer control,it being easy to use for example thermostats, digital thermometers,flowmeters, level alarms and/or optical devices to monitor the processand the formation of the desired solid solution. Computer control mayencompass step (7) or any number of further instant process steps, up tothe whole process including the manufacture of the first and secondcomponents. Computer control may be interrupted or assisted by manualoperation at critical stages.

Passing pigment suspension through a number of times in a circulating orshuttle mode of operation is understood to mean that the volume passedthrough is at least twice as great as the volume of the pigmentsuspension, which in the shuttle mode of operation corresponds topassing through approximately twice. The maximum value is arbitrary,although the use of more than one hundred passes, for example onethousand passes, whilst possible, is of little advantage because it hasno significant effect on the properties of the product. Circulating andshuttle modes of operation can also be used in alternance or combinedwith one another, for example grinding first in a circulating mode ofoperation and then in a shuttle mode of operation and vice versa.

In principle, the washing agents used in step (9) can be the same as instep (3).

Because the conditioning according to the invention is carried outsubstantially under neutral conditions, it is necessary to remove, atmost, very small amounts of acid or base. Moreover, once step (3) hasbeen carried out, most of the unreacted starting materials, reagents andby-products will already have been removed so that smaller amounts ofpolar solvents, for example alcohols and, preferably, water, can be usedfor the washing.

Isolation of the pigment is carried out by any desired known method. Forexample, it is possible to carry out filtration or centrifugation andthen to dry the moist material in an oven or fluidised-bed apparatus(for example at from 50 to 250° C., optionally in vacuo), or tofreeze-dry it. It is likewise possible to spray-dry the pigmentsuspension directly. The conditioned pigment is usually obtained in theform of a powder, which can, if desired, be dry-ground and sieved ortreated by any other desired physical method. However, it is perfectlypossible to store or use it as a wet filter cake, for example formanufacturing water-based masterbatches or coating compositions.

The organic liquid can for example be an alcohol, glycol, ether, amine,ketone, or an aliphatic or aromatic hydrocarbon; the organic liquid ispreferably neutral and comprises oxygen in its molecule, most preferablyit is a polar organic liquid having a dipole moment μ of 2.8-6.0·10⁻¹⁸esu. Neutral organic liquids are such having a pK_(a), respectivelyPK_(b), of about 5.5-8.5. The polar liquid advantageously has a dipolemoment μ of 2.8-6.0·10⁻¹⁸ esu (from 2.8 to 6.0 debye units), measured inbenzene at 25° C., preferably 3.3-5.5-10⁻¹⁸ esu, especially3.8-5.0·10⁻¹⁸ esu. The liquid should also be inert with respect to thepigment and to water at temperatures up to 100° C. and also, in theconcentration used and in the temperature range used, should dissolve inwater to give a clear solution, although that is virtually always thecase.

Suitable liquids are, for example, methanol, ethanol, n-propanol,isopropanol, n-butanol, isobutanol, 2-butanol, tert.-butanol or anyisomer of C₆-C₈ alcohols, acetone, ethylmethylketone, cyclohexanone.

Most suitable neutral polar liquids are, for example, acetamide,formamide, methyl-acetamide, methylformamide, caprolactam, valerolactam,1,1,2,2-tetramethylurea, dimethyl sulfoxide, sulfolane, nitromethane,nitrobenzene, acetonitrile, methanol, ethylene carbonate,dimethylacetamide, dimethylformamide and N-methylpyrrolidone, preferablydimethyl sulfoxide (DMSO), dimethylformamide (DMF) orN-methylpyrrolidone (NMP), especially N-methylpyrrolidone.

Of course, slight molecular modifications of the above-mentioned liquidsare possible (for example, replacement of methyl groups by ethyl groups)provided that their polarity remains suitable as a result. Optionally,it is also possible to use mixtures of a plurality of organic liquids,the overall polarity of which lies in the range of 2.8-6.0·10⁻¹⁸ esu, asa replacement for an organic liquid having a polarity in the same range(the overall polarity of a mixture of polar liquids, where applicable,should be calculated from the dipole moments of the components inproportion to the relative amounts thereof in the mixture).

The expression “liquid” is used herein because the pigments are, underneutral conditions, poorly soluble therein and therefore the usual term“solvent” would be functionally incorrect.

The amount of organic liquid in step (6) is advantageously from 0 to 30%by weight, based on the total amount of organic liquid and water.Preferably, there is no organic liquid or the amount of organic liquidis from 1 to 30% by weight, based on the total amount of organic liquidand water. Mixtures of organic liquids and water preferably form ahomogeneous phase, but this is not necessarily required provided that anaqueous phase is present (in the case of multiple liquid phases, theinstant definitions and preferences shall always apply to the aqueousphase, other phases containing no or less water shall be considered asadditional).

Preference is generally given to an amount of organic liquid of from 3to 20% by weight, especially from 5 to 10% by weight, based on the totalamount of organic liquid and water. However, a particularly preferredembodiment of the invention is to use from 0 to 3% by weight of liquid,based on the total amount of organic liquid and water. It is highlysurprising that the instant process works in the presence of only a verysmall amount of organic liquid or even in its total absence. When use insuch low amount, the organic liquid is adequately polar, otherwise itspresence will hardly have any influence on the process, as compared withplain water.

In addition, it is possible to use small amounts of additionalsubstances, for example acids, bases, resins, growth inhibitors, phasedirectors and, especially, viscosity improvers, dispersing agents and/orwetting agents. The amount of acid or base should, however, be at most0.01 mol, especially at most 0.001 mol, based on 1 mol of water. In theabsence or presence of only a small amount of organic liquid, theprocess is preferably operated in the presence of a small amount ofbase, most preferred at a pH in the range of from 9 to 11, especially ata pH of about 10. Resins (for example rosin, rosin derivatives, fattyamines or polyacrylates) are added in amounts of up to, at most, 10% byweight, preferably at most 5% by weight, especially 1% by weight, basedon the pigment. Growth inhibitors, phase directors, viscosity improversand dispersing agents are known to the person skilled in the art and maybe, for example, substances having structural elements of the pigment;they are usually used in amounts of at most 0.2 mol, preferably at most0.1 mol, most preferred at most 0.03 mol, based on 1 mol of pigment.Wetting agents, for example cationic, anionic, amphoteric or non-ionicwetting agents, can likewise be added in customary amounts. Preferenceis given, in that case, to the addition of from 0.2 to 5% by weight,especially from 0.5 to 3% by weight, based on the pigment, of anamphoteric wetting agent. Additional substances in general can suitablybe added in any step (1), (2), (3), (5), (6), (7), (8) or (9),preferably in step (7), (8) or (9), with particular preference in step(7), especially after two-third of the total duration of step (7).However, it is preferred to add phase directors before or in an earlystage of step (7), and growth inhibitors as well as viscosity improversafter or in a late stage of step (7), at which time it is also mostadequate, if desired, to perform any usual surface treatment to improverheology, dispersibility and/or other applicatory properties. Early andlate stage can be understood to be the first, respectively the lastthird of the total grinding time, preferably the first, respectively thelast fifth of the total grinding time.

A major advantage of the invention is that no solid salts are necessary.Although it is possible to add salts (for example sodium chloride orsodium sulfate) up to the saturation limit in the aqueous liquid, thatdoes not bring about any advantages but, on the contrary, only givesrise to additional problems in recovering the liquid.

The method can be performed in the presence of air. In the case ofoxidisable pigments, for example quinacridones, it is, however,advantageously possible, if desired, to create inert conditions verysimply using nitrogen, carbon dioxide or a noble gas.

It is self-evident that, for the purpose of recycling, the organicliquid used can be recovered by methods known per se, for example bydistillation. Dilute aqueous solutions of organic liquids areconveniently disposed of for example by wet oxidation.

In contrast to other conditioning methods, for example kneading, theviscosity plays a rather subordinate role. It is necessary, however, toselect a viscosity range that is suitable for the apparatus used, forexample from 5·10⁻² Pa·s to 5 Pa·s, preferably from 10⁻¹ Pa·s to 5·10⁻¹Pa·s (at 500 s⁻¹). The person skilled in the art will know, or candetermine by simple means known to him, how the viscosity depends uponthe temperature, the liquid selected and the concentration thereof, andupon the concentration and particle shape of the pigment beingconditioned.

The amount of crude pigments is usually, in step (7), from 1 to 25% byweight, preferably from 2 to 20% by weight, especially from 5 to 15% byweight, based on the total amount of crude pigments, liquid and water(including water or liquid in the press cake), it being necessary ofcourse for the amount of crude pigments to be calculated from the crudepigment content of the press cakes when the press cakes are not dried.The amount of crude pigment in a press cake is usually from 10 to 50% byweight, preferably from 20 to 40% by weight, based on the wet presscake.

The first component and the second component of the instant solidsolutions can be individual chemical compounds, mixtures of a pluralityof chemical compounds or even solid solutions or mixed crystalscomprising a plurality of chemical compounds, preferably quinacridonesand/or diketopyrrolopyrroles, optionally in combination with derivativesthereof. Of course, the solid solutions or mixed crystals used ascomponents are different from the solid solutions or mixed crystalsinstantly to be produced in that they lack the other instant componentor comprise a different amount of it. For example, it is possible toproduce a ternary solid solution from a binary solid solution and asingle component, or a mixed crystal may be made from a solid solutionand an additional amount of one of its components, thus adjusting themolar ratio precisely to the value required by the mixed crystal'slattice (or vice versa). Of course, the solid solutions or mixedcrystals made by the instant process may themselves also be used ascomponents for making further solid solutions or mixed crystals.

Additionally to the first component and the second component, it isoptionally also possible to use further components to be incorporatedinto the instant solid solution as well, for example a third, or also afourth and even a fifth component. These components are then alsoincluded in step (7) and preferably in steps (1) to (6), too. Usually,solid solutions have no more than five components so that it will not benecessary to use more than five components, but the invention clearlyalso encompasses the production of solid solutions or mixed crystalshaving an unlimited number of components. It is adequate both to mix allthe components together simultaneously or in sequence, the latterprocedure being especially useful when the number of components exceedsthe number of available vessels or when it is intended to mix thecomponents by manual control.

In the selection of components and the amounts thereof, the personskilled in the art will take as target solid solutions or mixed crystalsthat are known per se or to be expected on the basis of the state of theart and use components which are known and easily accessible, but notnecessarily having excellent pigmentary properties.

The shuttle mode of operation is especially well suited. The number ofstorage vessels is, in such a case, preferably one more than the numberof components, which makes it possible for the treatment period to bematched to the characteristics of the different components and the solidsolution or mixed crystal to be obtained. The person skilled in the artwill immediately recognise the great advantages of this method.

The second component of the instant solid solutions is, for example,from the 1-aminoanthraquinone, anthanthrone, anthrapyrimidine, azo,azomethine, dioxazine, diketopyrrolopyrrole, flavanthrone, indanthrone,isoindoline, isoindolinone, isoviolanthrone, perinone, perylene,phthalocyanine, pyranthrone, quinacridone, quinacridonequinone,quinophthalone or thioindigo series, optionally also in the form ofmetal complexes or metal lakes. The second component is preferably alsoselected from the group consisting of4,4′-diamino-1,1′-dianthraquinonyls, diketopyrrolo[3,4-c]pyrroles,triphenedioxazines, indanthrones, perylenes, phthalocyanines andquinacridones, most preferably of the same member of this group, as thefirst component.

Solid solution pigments obtainable according to the invention compriseas individual components, for example, Colour Index Pigment Yellow 24,108, 109, 110, 123, 147, 173, 193, 199, Pigment Orange 40, 43, 48, 49,51, 61, 71, 73, Pigment Red 88, 89, 122, 149, 168, 177, 178, 179, 181,190, 192, 194, 202, 204, 206, 207, 209, 216, 224, 226, 254, 255, 262,264, 270, 272, Pigment Violet 19, 23, 29, 31, 37, 42, Pigment Blue 15,15:1, 15:2, 15:3, 15:4, 15:6, 16, 60, 64, Pigment Green 7, 36, PigmentBlack 31, 32, Vat Red 74,3,6-di(3′-cyano-phenyl)-2,5-dihydro-pyrrolo-[3,4-c]pyrrole-1,4-dione or3-phenyl-6-(4′-tert-butyl-phenyl)-2,5-dihydro-pyrrolo-[3,4-c]pyrrole-1,4-dione,of which preferably those selected from the group consisting of4,4′-diamino-1,1′-dianthraquinonyls, diketopyrrolo[3,4-c]pyrroles,triphenedioxazines, indanthrones, perylenes, phthalocyanines andquinacridones.

Special preference is given to polycyclic components, including,especially, quinacridones, perylenes and diketopyrrolopyrroles, veryespecially quinacridones preferably being prepared by oxidation ofdihydroquinacridones using hydrogen peroxide, for example as describedin U.S. Pat. No. 5,840,901 or U.S. Application 60/277,824.

The instant method is especially excellent to prepare solid solutionscomprising as components two quinacridones or a quinacridone and adiketopyrrolo[3,4-c]pyrrole, preferably comprising unsubstitutedquinacridone and 2,9-dichloroquinacridone, unsubstituted quinacridoneand 3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione,unsubstituted quinacridone and3,6-di(4′-chloro-phenyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione,2,9-dichloroquinacridone and3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione,2,9-dichloroquinacridone and3,6-di(4′-chloro-phenyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione or3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione and3,6-di(4′-chloro-phenyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione,most preferred comprising unsubstituted quinacridone and2,9-dichloroquinacridone, unsubstituted quinacridone and3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione or2,9-dichloro-quinacridone and3,6-di(4′-chloro-phenyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione.

The solid solution pigments obtained in accordance with the inventionhave a high degree of crystallinity and optimum fastness properties, aswell as high colour strength and colour saturation. Moreover, theparticle size distribution is astonishingly narrow. In the case of thepreferred average particle size of the conditioned pigment {overscore(L)} of preferably from 0.01 to 3 μm, especially from 0.05 to 2 μm, atleast 90% by weight of particles have a size of L±½{overscore (L)} (forexample, in the case of an average particle size of 0.2 μm, 0.2±0.1μm=0.1 to 0.3 μm). Especially, at least 80% by weight of particles havea size of L±¼{overscore (L)}.

Solid solutions and mixed crystals are easily identifiable from physicalmixtures of their components by their X-ray powder diagrams. Preferenceis given to carrying out the method at least until the pigment consistsof a single uniform crystalline phase (solid solution or mixed crystal)or at least one component can essentially no more be identified on theX-ray powder diagram.

The pigments obtained according to the invention can be used for allcustomary purposes, for example for mass-coloration of polymers,including polymers in the form of fibres, surface-coatings (includingspecial-effect paints, including those for the automobile sector) andprinting inks, or also in so-called resists or as toners. Suchapplications will be so evident to the person skilled in the art thatthey need not be listed here. They are also disclosed in referenceworks, for example “Industrielle Organische Pigmente” (W. Herbst+K.Hunger, VCH Weinheim/N.Y., new editions being continually published inGerman and English).

It is also advantageously possible to prepare both transparent andhiding forms. Especially advantageous is the preparation of hidingpigments. The hiding power is suitably measured in a 25±5 μm thickacrylic or polyester enamel coating system having a pigment to binderweight ratio of 0.18 over a black and white background and prepared andmeasured according to established industry procedures such as disclosedin Example 10. For a hiding pigment, the color difference ΔE* measuredover a black and white background should be less or equal to 15,preferably ≦10, most preferably ≦5.

Transparent pigments generally have a particle size (length) of0.001-0.3 μm, preferably 0.01-0.2 μm, most preferably combined with thenarrow particle size distribution mentioned above. In the same coatingas above, the color difference ΔE* measured over a black background isadvantageously less or equal to 15, preferably ≦10, most preferably ≦5,as compared with the color of the black background itself.

It has furthermore been found, that pigments prepared in accordance withthe invention are of such outstanding quality that they may frequentlycome into consideration for applications where the qualities obtainablehitherto for the same solid solution pigment have not been entirelysatisfactory. The person skilled in the art is here expresslyrecommended to carry out appropriate experiments.

The Examples that follow illustrate the invention, without limiting thescope thereof (unless otherwise specified, “%” is always % by weight):

EXAMPLE 1

Unsubstituted γ-quinacridone is prepared in accordance with Example 1 ofU.S. Pat. No. 5,840,901, but without drying after washing with warmwater. Using water, a portion of the wet press cake containing 33.33 gof quinacridone is flushed into a storage vessel and slurried (totalweight of the suspension: 400 g). 2,9-Dichloro-quinacridone is preparedin accordance with Example 3 of U.S. Pat. No. 5,840,901, but withoutdrying after washing with warm water. Using water, a portion of the wetpress cake containing 66.67 g of 2,9-dichloroquinacridone is flushedinto a storage vessel and slurried (total weight of the suspension: 600g). Both storage vessels are heated to 35° C. The γ-quinacridone is thenpassed, via a cylindrical wet mill (volume corresponding to 24 parts byweight of water), filled to about 80% of its volume with mixed zirconiumoxide grinding elements from 0.3 to 0.4 mm in diameter, at a radialspeed of 10 m·s⁻¹, into the 2,9-dichloroquinacridone suspension, and themixture is passed back and forth between the two storage vessels in ashuttle mode of operation for 1 hour. The first storage vessel is thenrinsed with 120 g of N-methylpyrrolidone and a circulating mode ofoperation is carried out using the second storage vessel for a further 1hour at a radial speed of 13.5 m·s⁻¹ and a temperature of 95° C. Theradial speed is then reduced to 4.0 m·s⁻¹ and the suspension is groundfor a further 1 hour in circulating mode. The product is then filteredand washed and dried in customary manner. A quinacridone solid solutionpigment having a narrow particle size distribution and excellentapplication properties is obtained.

EXAMPLE 2

A mixture of 750 g crude 2,9-dichloroquinacridone and 250 g crudeunsubstituted quinacridone (both obtained as coarse particles ofspecific surface area about 10 m²/g by oxydation of the corresponding6,11-dihydroquinacridones) are stirred in 1020 g of water for 2 hoursand then, analogously to Example 1 above, transferred to a storagevessel using 60 g of N-methylpyrrolidone and heated to 70° C. Thesuspension is circulated through a cylindrical wet mill (volume 460cm³), filled to about 85% of its volume with yttrium-stabilised mixedzirconium oxide grinding elements from 0.3 to 0.4 mm in diameter, at aradial speed of 12 m·s⁻¹ (speed of rotation 3000 rpm) and a nominalpower output of 0.50 kj·s⁻¹ for 6 hours at constant temperature. Thenominal power output is reduced to 0.1 kj·s⁻¹ (speed of rotation 1800rpm) and the temperature is lowered to 25° C. over the course of 1 hour.The suspension is filtered under suction and washed twice, using 2.0 kgof water each time; the product is dried at 80° C./2·10³ Pa. A fine,strongly coloured quinacridone solid solution pigment having a narrowparticle size distribution and excellent application properties isobtained.

EXAMPLE 3

A wet press cake of1,4-diketo-2,5-dihydro-3,6-di(4-tert.-butyl-phenyl)-pyrrolo[3,4c]pyrrolecontaining 180 g of dry pigment is flushed and slurried with water intoa storage vessel (total weight of the suspension: 1660 g). In a secondstorage vessel, a wet press cake of1,4-diketo-2,5-dihydro-3,6-di(4-chloro-phenyl)-pyrrolo[3,4c]pyrrolecontaining 270 g of dry pigment is flushed and slurried with water(total weight of the suspension 2490 g). The contents of both storagevessels (totally 4150 g, 10.8 weight-% solids) are mixed together andthe mixed suspension is then passed into an empty vessel, via acylindrical wet mill, filled to about 80% of its volume with mixedzirconium oxide grinding elements from 0.3 to 0.4 mm in diameter, at aradial speed of 10 m·s⁻¹. Then, the mixture is passed back and forthbetween the two storage vessels in a shuttle mode of operation for 1hour. The first storage vessel is then rinsed with 100 g of water andthe process is carried on in a circulating mode of operation using onlythe second storage vessel for further 4 hours at a radial speed of 13.5m·s⁻¹ and a temperature of 30° C. At the end of the milling, the mill isrinsed out with 300 g of water and the rinsing water is added to themixed crystal pigment dispersion. For ripening the pigment, 350 g of1-butanol are then added to the suspension and the temperature is keptat 92° C. for 1 hour. The product is finally filtered, washed and driedin customary manner. A mixed crystal diketopyrrolopyrrole pigment havinga narrow particle size distribution and excellent application propertiesis obtained.

EXAMPLE 4

The procedure is analogous to Example 3, but the ripening with butanolis omitted. Alternatively, the ripening conditions can also be variedwithin very large limits (for example the ripening temperature and/ortime such as disclosed in the following examples) depending on thedesired final particle size.

EXAMPLE 5

The procedure is analogous to Example 3, but the ripening time isdecreased to only 0.5 hour. A pigment of smaller particle size andincreased transparency is obtained.

EXAMPLE 6

The procedure is analogous to Example 3, but the ripening time isincreased to 4 hours. A pigment of bigger particle size and increasedopacity is obtained.

EXAMPLE 7

The procedure is analogous to Example 3, but the ripening temperature isdecreased to 40° C. A pigment of smaller particle size and increasedtransparency is obtained.

EXAMPLE 8

The procedure is analogous to Example 3, but the ripening temperature isincreased to 115° C. (using a pressure-proofed closed equipment). Apigment of bigger particle size and superior opacity is obtained.

EXAMPLE 9

Unsubstituted γ-quinacridone is prepared in accordance with Example 1 ofU.S. Pat. No. 5,840,901, but without drying after washing with warmwater. Using water, a portion of the wet press cake containing 33.33 gof quinacridone is flushed into a storage vessel and slurried (totalweight of the suspension: 400 g). 2,9-Dichloro-quinacridone is preparedin accordance with Example 3 of U.S. Pat. No. 5,840,901, but withoutdrying after washing with warm water. Using water, a portion of the wetpress cake containing 66.67 g of 2,9-dichloroquinacridone is flushedinto a storage vessel and slurried (total weight of the suspension: 600g). Both storage vessels are heated to 35° C. The γ-quinacridone is thenpassed, via a cylindrical wet mill (volume corresponding to 24 parts byweight of water), filled to about 80% of its volume with mixed zirconiumoxide grinding elements from 0.3 to 0.4 mm in diameter, at a radialspeed of 10 m·s⁻¹, into the 2,9-dichloroquinacridone suspension.Afterwards, the first storage vessel is then rinsed with 500 g of waterand a circulating mode of operation is carried out using the secondstorage vessel for further 4 hours at a radial speed of 13.5 m·s⁻¹ and atemperature of 35° C. The radial speed is then reduced to 4.0 m·s⁻¹ andthe suspension is further ground for 1 hour in circulating mode at atemperature of 95° C. The product is then filtered and washed and driedin customary manner. A quinacridone solid solution pigment having anarrow particle size distribution and excellent application propertiesis obtained.

EXAMPLE 10

The pigment according to Example 1 is incorporated into an automotivepolyester/CAB enamel paint system. 41.0 CAB ® 531.1 (Eastman Chem.), 20%cellulose acetobutyrate in butyl acetate/xylene 2:1 1.5 NUODEX ® 6(zirkonium octoate, Nordmann, Rassmann, D-Hamburg) 18.5 Solvesso ® 150(Exxon) 21.5 butyl acetate 17.5 xylene(b) Millbase Formulation:

A 250 ml jar is charged with 15.73 g Dynapol® H 700-08 (Degussa-Hüls),11.80 g of the freshly prepared binder solution from (a), 11.80 gMaprenal® MF 650 (Vianova Resins) and 2.67 g dispersant Disperbyk® 161(BYK Chemie). 8 g pigment according to Example 1 and 100 g of glassbeads are added. The mixture in the jar is shaken on a Skandex shakerfor 1 hour. The millbase contains 16.0% pigment with a pigment/binderratio of 1:2.25 and a solids (pigment+binder) content of 59%.

(c) Masstone Color for an PES/CAB Enamel Drawdown:

23.75 g of the millbase from (b), 10.50 g of Dynapol® H 700-08, 7.87 gof the binder solution from (a) and 7.87 g Maprenal® MF 650 are mixed,yielding a resin/pigment dispersion with a concentration of 7.6% pigmentin a pigment to binder ratio of 1:5.22 and a solid (pigment+binder)content of 47,3%.

(d) Coating:

The resin/pigment dispersion is drawn down onto a Leneta black and whitechart from the Leneta Company using a 100 μm wet film applicator. Thefilm is flashed in a flash cabinet for 30 minutes and then “baked” in anoven at 130° C. for 30 minutes. The final thickness of the coating is 28μm.

(e) Colour Measurement:

The C.I.E. L*, C*, h color space values are obtained from the portionover white background using a D₆₅ illuminant and 10° observer with aspecular component included.

EXAMPLES 11-18

The procedure is analogous to Example 10 (a)-(e), but the pigment ofExample 1 is replaced by the pigments of Examples 2-9.

Instead of a masstone, it is also possible to make metallic orgoniochromatic, optionally two-coat coatings with excellent results, inparticular when using instant pigments of high transparency.

1. A method for the preparation of a conditioned organic pigmentcomprising at least a first component selected from the group consistingof 4,4′-diamino-1,1′-dianthraquinonyls, diketopyrrolo[3,4-c]pyrroles,triphenedioxazines, indanthrones, perylenes, phthalocyanines andquinacridones, and a second component forming a solid solution or amixed crystal with the first component, the molar ratio of the firstcomponent to the second component in the solid solution or mixed crystalbeing greater or equal to 1, wherein (1) the first component and thesecond component are each independently from the other so synthesisedthat they precipitate from a liquid reaction mixture, and a pigmentsuspension is formed in the liquid reaction medium; (2) optionally, theconcentration of pigment in one or both pigment suspensions from step(1) is increased by removing all or part of the liquid reaction medium;(3) optionally, a washing agent is added once or more than once and thenthe concentration of pigment in one or both pigment suspensions fromstep (1) or (2) is increased by removing all or part of the liquidphase; (4) optionally, the pigment suspension is dried; (5) the pigmentsuspensions from step (1), the concentrated pigment suspensions fromstep (2), or the pigment suspensions (treated with a washing agent andconcentrated) from step (3), the liquid phases of which consistsubstantially of water, an organic liquid or a mixture thereof, or thedried pigments from step (4) are each transferred into a storage vesselor both transferred into the same storage vessel, optionally withaddition of water or an organic liquid; (6) if the liquid phase of thepigment suspension in one or both storage vessels does not alreadyconsist of water and optionally an organic liquid, the amount of organicliquid being from 0 to 50% by weight, based on the total amount oforganic liquid and water, the composition of the pigment suspension isso modified by means of the addition of water that the amount of organicliquid is from 0 to 50% by weight, based on the total amount of organicliquid and water; and/or optionally organic liquid is added in suchquantity that its total amount does not excede 50% by weight, based onthe total amount of organic liquid and water; (7) the pigment suspensionfrom the storage vessel containing the first component and if applicablethe pigment suspension from the storage vessel containing the secondcomponent are passed a number of times through an agitated media pearlmill in a circulating or shuttle mode of operation, the agitated mediapearl mill having a smaller chamber volume than the volume of thepigment suspension and being operated at a specific power density of atmost 2.0 kJ·s⁻¹ per litre of grinding space, whereby in case of morethan one storage vessel the flow between the storage vessels and thepearl mill is controlled in such a way that the contents of all storagevessels are mixed together at any stage up to before the last pass inthe pearl mill; whereby the first component and the second componentcombine to form a solid solution or a mixed crystal; (8) optionally, theconcentration of pigment in the pigment suspension from the agitatedmedia pearl mill is increased by removing all or part of the liquidreaction medium; (9) optionally, a washing agent is added once or morethan once to the pigment suspension from step (7) or (8) and then theconcentration of pigment in the pigment suspension is increased byremoving all or part of the liquid phase; and (10) optionally, thepigment is isolated by removing the liquid surrounding it.
 2. A methodfor the preparation of a conditioned pigment according to claim 1,wherein the second component is selected from the group consisting ofthe 1-aminoanthraquinones, anthanthrones, anthrapyrimidines, azos,azomethines, dioxazines, diketopyrrolopyrroles, flavanthrones,indanthrones, isoindolines, isoindolinones, isoviolanthrones, perinones,perylenes, phthalocyanines, pyranthrones, quinacridones,quinacridonequinones, quinophthalones or thioindigos.
 3. A method forthe preparation of a conditioned pigment according to claim 1, whereinthe first component is selected from the group consisting ofquinacridones, perylenes and diketopyrrolopyrroles.
 4. A methodaccording to claim 1, wherein the first component and the secondcomponent are both 4,4′-diamino-1,1′-dianthraquinonyls, bothdiketopyrrolo[3,4-c]pyrroles, both triphenedioxazines, bothindanthrones, both perylenes, both phthalocyanines or bothquinacridones.
 5. A method according to claim 1, comprising twoquinacridones or a quinacridone and a diketopyrrolo[3,4-c]pyrrole.
 6. Amethod according to claim 1, wherein the organic liquid is neutral andcomprises oxygen in its molecule.
 7. A method according to claim 1,wherein the organic liquid has a dipole moment μ of 2.8-6.0·10⁻¹⁸ esu.8. A method according to claim 1, wherein the organic liquid is selectedfrom the group consisting of acetamide, formamide, methylacetamide,methylformamide, caprolactam, valerolactam, 1,1,2,2-tetramethylurea,dimethyl sulfoxide, sulfolane, nitromethane, nitrobenzene, acetonitrile,methanol, ethylene carbonate, dimethylacetamide, dimethylformamide andN-methylpyrrolidone, or is a mixture of a plurality of organic liquids,the overall polarity of which lies in the range of 2.8-6.0·10⁻¹⁸ esu. 9.A method according to claim 1, wherein the amount of organic liquid isfrom 1 to 30% by weight based on the total amount of organic liquid andwater.
 10. A method according to claim 1, wherein the amount of organicliquid is from 0 to 3% by weight of liquid, based on the total amount oforganic liquid and water.
 11. A method according to claim 1, wherein thetemperature of the suspension in the pearl mill is at the beginning ofstep (7) from 10 to 50° C. and at the end of step (7) from 30 to 100° C.12. A method according to claim 1, wherein an additional substanceselected from the group consisting of acids, bases, resins, growthinhibitors, phase directors, dispersing agents and wetting agents isadded in any step (1), (2), (3), (5), (6), (7), (8) or (9).
 13. A methodaccording to claim 1, wherein the total treatment period in the agitatedmedia pearl mill is from 10 to 600 minutes.
 14. A method according toclaim 13, wherein after two-third of the total treatment period, theradial speed is adjusted to a value of at most 11 m·s⁻¹.
 15. A methodaccording to claim 1, wherein the pigment obtained in step (10) consistsof at least 90% by weight of particles have a size of L±½{overscore(L)}, wherein the average particle size {overscore (L)} is from 0.01 to3 μm.
 16. A method according to claim 1, wherein the pigment obtained instep (10) is hiding and leads to a color difference ΔE* less or equal to15, measured in a 25±5 μm thick acrylic or polyester enamel coatingsystem having a pigment to binder weight ratio of 0.18 over a black andwhite background.
 17. A method according to claim 1, wherein the pigmentobtained in step (10) is transparent and has a particle size of0.001-0.3 μm.
 18. A method according to claim 1, comprisingunsubstituted quinacridone and 2,9-dichloro-quinacridone, unsubstitutedquinacridone and3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione, unsubstitutedquinacridone and3,6-di(4′-chloro-phenyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione,2,9-dichloroquinacridone and3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione,2,9-dichloroquinacridone and3,6-di(4′-chloro-phenyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione or3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione and3,6-di(4′-chloro-phenyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione.19. A method according to claim 1 wherein the amount of organic liquidis from 0 to 3% by weight of liquid, based on the total amount oforganic liquid and water, at a pH in the range of from 9 to
 11. 20. Amethod according to claim 1, wherein the pigment obtained in step (10)is hiding and leads to a color difference ΔE* less or equal to 10,measured in a 25±5 μm thick acrylic or polyester enamel coating systemhaving a pigment to binder weight ratio of 0.18 over a black and whitebackground.